feat: new value source types (HA entity, gradient map, strip extract) + UI fixes

New value source types:
- ha_entity: reads numeric values from HA entity state/attribute, normalizes
  via min/max range, applies EMA smoothing. EntitySelect for HA connection
  and entity selection with live entity list fetching.
- gradient_map: maps a float value source (0-1) through a gradient entity.
  EntitySelect for both input source and gradient with inline previews.
- css_extract: extracts single color by averaging LED range from a color
  strip source. EntitySelect for source selection.

Value source type picker:
- Filter tabs (All / Numeric / Color) above the icon grid
- showTypePicker extended with filterTabs + onFilterChange support

Palette selectors converted to EntitySelect:
- Effect palette, gradient preset, and audio palette selectors now use
  command-palette style EntitySelect with gradient strip previews

Tab indicator fixes:
- Icon now updates on tab switch (was passing no args to updateTabIndicator)
- Visible with any background effect active, not just Noise Field
- Noise Field is the default background effect for new users

Dashboard section collapse fix:
- Split header into clickable toggle (chevron+label) and non-clickable
  actions area — buttons no longer trigger collapse/expand

Discriminated union fix (422 errors):
- source_type/target_type now always included in update payloads for:
  CSS editor, LED target, HA light target, simple calibration,
  advanced calibration

server/src/wled_controller/static/js/features/dashboard.ts

@@ -354,10 +354,12 @@ function _sectionHeader(sectionKey: string, label: string, count: number | strin
     const collapsed = _getCollapsedSections();
     const isCollapsed = !!collapsed[sectionKey];
     const chevronStyle = isCollapsed ? '' : ' style="transform:rotate(90deg)"';
-    return `<div class="dashboard-section-header" data-dashboard-section="${sectionKey}" onclick="toggleDashboardSection('${sectionKey}')">
-        <span class="dashboard-section-chevron"${chevronStyle}>&#9654;</span>
-        ${label}
-        <span class="dashboard-section-count">${count}</span>
+    return `<div class="dashboard-section-header" data-dashboard-section="${sectionKey}">
+        <span class="dashboard-section-toggle" onclick="toggleDashboardSection('${sectionKey}')">
+            <span class="dashboard-section-chevron"${chevronStyle}>&#9654;</span>
+            ${label}
+            <span class="dashboard-section-count">${count}</span>
+        </span>
         ${extraHtml}
     </div>`;
 }